Constant radius single photon emission tomography

ABSTRACT

A nuclear camera ( 10 ) includes four or more gamma detectors ( 20, 20′, 20″, 201, 202, 203, 204, 205, 206 ) arranged or, a generally circular rotatable gantry ( 12, 12′, 12″, 12 ′″) around an imaging region that emits emission radiation. The gamma detectors are each disposed at a fixed equal distance (R, R 2,  R 3 , R 5 ) from an imaging isocenter ( 22, 22′, 22′, 22 ″) to rotate in a fixed radius circular orbit. Each gamma detector includes a radiation sensitive surface ( 72 ) that responds to the emission radiation and a slat collimator ( 70 ) that spins about an axis  88.  Resolution and sensitivity at the fixed radius are selected by selecting collimator slat height (Wz) and spacing (G) and radiation sensitive surface width (Cy). The gamma detectors and rotating gantry are enclosed in an optically opaque toroidal housing ( 14 ) that defines a generally circular bore ( 16 ) that admits imaging subjects over a range of sizes.

The following relates to the diagnostic imaging arts. It particularlyrelates to single photon emission computed tomography (SPECT) imaging,and will be described with particular reference thereto. However, it mayfind application in other diagnostic imaging modalities.

Nuclear cameras typically employ one to three gamma detectors mounted ona linear positioning element that is in turn mounted to a rotatinggantry. The rotating gantry moves the gamma detector angularly about theregion of interest, while the linear positioning element moves the gammadetector radially toward or away from a region of interest to produce aconformal non-circular orbit that closely follows external contours ofan imaging subject. In another arrangement, the gamma detectors aremounted on robotic arms that provide both rotational and radial detectormovement to effect conformal non-circular orbiting.

Each gamma detector includes a scintillator that is viewed by an arrayof photomultiplier tubes. A radiation particle strikes the scintillatorand produces a flash of light. Nearby photomultiplier tubes detect theresultant scintillation event. The particle energy and position on thedetector are computed based on the photomultiplier tube outputs. Acollimator, which is typically a lead plate with an array of bores, ismounted on the gamma detector between the scintillation crystal and theimaged subject to define linear projection views. A detector of thistype isolates a scintillation event as originating along a ray or lineof view, or more precisely along a narrow-angle cone of view, defined bythe axis of the collimator bore.

Another type of gamma detector employs a slat collimator. The slatcollimator includes generally parallel collimating slats that defineplane integral projection views. Sensitivity is improved by receivingradiation over a band rather than a narrow-angle cone. Someslat-collimated gamma detectors employ semiconductor-based radiationdetectors, such as a cadmium zinc telluride (CZT) detectors. To enablespatial location along the bands to be resolved, the slats are spun orrotated during imaging about an axis transverse to the detector face, sothat plane integral projections over at least 180°, and preferably 360°,of planar orientations are collected for each gantry angular view.Slat-collimated detectors, defining planes of activity instead on linesof activity, have certain advantages including improved signalsensitivity.

As the gamma detectors conformally orbit the imaging subject, linearprojection data is acquired over an angular range of projection views,which are then reconstructed into a three-dimensional image. For medicalimaging, a radiopharmaceutical or radioisotope such as ^(99m)Tc or ²⁰¹T1is introduced into the subject. The radioisotope distributes over thecirculatory system or accumulates in an organ of interest whose image isto be produced. To minimize radiation exposure of the subject, the doseof administered radiopharmaceutical and its associated half-life arelimited. This in turn leads to low radiation signal strength, lowsignal-to-noise ratios, and temporally limited imaging windows.

To counteract these signal limitations, special attention should begiven to optimizing the number of collected counts, that is, thesensitivity, as well as their quality, that is, spatial resolution.Non-circular contoured orbits of the gamma detectors about the subjectsubstantially improves resolution and sensitivity by minimizing adistance between each gamma detector and the imaging subject.

However, contoured non-circular gamma detector orbits have certaindisadvantages. Determining the precise contoured orbit, which issubject-specific, increases imaging preparation time. The number ofgamma detectors on the gantry is generally limited by the conformalorbiting to three or fewer detectors. A larger number of detectors isnot readily simultaneously conformally arranged in close proximity tothe imaging subject. Additionally, contoured movement of large gammadetector heads in close proximity to a human imaging subject isintimidating, particularly for head scans. Conformal orbiting alsoprecludes shielding of the moving parts from the subject's view using agantry enclosure or gamma camera housing. Image reconstruction is alsocomplicated by conformal orbiting, since non-circular orbiting destroysadvantageous spatial symmetries, adds a radius dependency to the data,and thus increases image reconstruction complexity and time.

The present invention contemplates an improved apparatus and method thatovercomes the aforementioned limitations and others.

According to one aspect, a nuclear camera is disclosed. A rotatablegantry defines a gantry rotation axis and an imaging isocenter. A gammadetector is arranged on the rotating gantry at a fixed radial distancefrom the imaging isocenter. The gamma detector includes aradiation-sensitive surface and a collimator that collimates incomingradiation.

According to another aspect, a nuclear camera is disclosed. At leastone, up to six or more, but optimally four SPECT radiation detectors arerotatably arranged around an imaging region to receive emissionradiation. The radiation detectors are each disposed an equal distancefrom an imaging isocenter. The radiation detectors each include aradiation-sensitive surface that responds to the first emissionradiation. A slat collimator is disposed on each radiation detectorbetween the radiation detector and the imaging region to provide planarcollimation of incoming first emission radiation. A means is providedfor spinning the collimator and radiation-sensitive surface of eachSPECT radiation detector about a detector axis.

According to yet another aspect, a radiological imaging method isprovided. At least one radiation detector is circularly orbited about animaging volume at a fixed radial distance from a first axis of rotationthrough the imaging volume. Radiation from the imaging volume isdetected at a generally planar radiation-sensitive region of theradiation detector. The radiation-sensitive region faces the imagingvolume during the fixed radius circular orbiting.

One advantage resides in elimination of the detector orbit-contouringstep in a nuclear imaging session.

Another advantage resides in providing four or more simultaneouslyoperating gamma detectors on a single rotating nuclear camera gantry.

Yet another advantage resides in inclusion of an enclosing gantryhousing surrounding a rotating nuclear camera gantry that protectsmoving parts such as the rotating gantry and the gamma detectors, andthat blocks the moving parts from view of the imaging subject and makingthe nuclear imaging device comport in aspect, shape, and size with othermedical imaging devices such as PET, CT, or MRI.

Still yet another advantage resides in providing imaging using acircular orbit that has a high degree of symmetry which can be used tosimplify image reconstruction processing and reduce image reconstructiontime.

Numerous additional advantages and benefits will become apparent tothose of ordinary skill in the art upon reading the following detaileddescription of the preferred embodiments.

The invention may take form in various components and arrangements ofcomponents, and in various process operations and arrangements ofprocess operations.

The drawings are only for the purpose of illustrating preferredembodiments and are not to be construed as limiting the invention.

FIG. 1 shows a perspective view of a multiple imaging modalityradiological imaging apparatus including a gamma camera with gammadetectors that orbit an imaging region on an enclosed gantry at aconstant circular viewing radius.

FIG. 2 shows a perspective view of a slat-collimated gamma detector.

FIG. 3 diagrammatically shows arrangement of four gamma detectors at aconstant viewing radius on the circular gantry of the gamma camera ofFIG. 1.

FIG. 4 diagrammatically shows six slat-collimated gamma detectors on asingle constant-radius gantry, in which each of the slat-collimatedgamma detectors acquires data over a selected sub-set of slat angularorientations.

FIG. 5 diagrammatically shows a single-gantry SPECT/PET system.

FIG. 6 diagrammatically shows a single-gantry SPECT/CT system.

With reference to FIG. 1, a multiple imaging modality radiologicalimaging system 8 is shown. A nuclear camera 10 includes a generallycircular rotatable gantry 12 disposed in a generally toroidal stationaryhousing 14. The housing 14 defines a stationary generally cylindricalbore 16 inside of which an imaging subject is disposed. The housingportion that defines the stationary bore 16 is optically opaque, butgenerally transmissive for gamma radiation toward the bore. An imagingsubject is moved into the bore 16 using a subject support couch 18. Atleast one gamma detector 20 (shown by partial cutaway of the enclosinghousing 14) is disposed on the rotating gantry 12 and rotates therewith.

The gamma detector 20 rotates in a circular orbit of viewing radius Rabout an isocenter 22 of an imaging region inside the bore 16. However,a human subject disposed in the bore 16 is prevented by the housing 14from observing the moving components of the gamma camera 10, such as thegantry 12 and gamma detector or detectors 20, because the housing 14 isoptically opaque. Moreover, the circular gamma detector viewing orbitradius R is substantially larger than a minimum radius of a conformalnon-circular gamma detector orbit of the type heretofore used in nuclearimaging. This allows the bore 16 to be made large enough to admitsubjects of varying sizes. For medical imaging, the bore 16 ispreferably large enough to admit a human subject of substantially anysize, e.g. a 60 cm diameter.

With continuing reference to FIG. 1, the radiation detector or detectors20 of the gamma camera 10 acquire plane integral projection views thatare stored in a projection memory 30. The plane integral projectionviews are processed by a reconstruction processor 32 to reconstruct athree-dimensional image representation of the imaging region. Onesuitable reconstruction employs an inverse Radon transform. Thereconstructed image is stored in an image memory 34.

The reconstructed image is processed by a video processor 36 anddisplayed on a user interface 38 for review by a radiologist or otheruser. The user interface 38 preferably includes a high resolution videodisplay, a keyboard, a mouse or other pointing device, and the like. Thereconstructed image can also be processed by a printer driver andprinted, communicated over a hospital network or the Internet, orotherwise manipulated. Preferably, the user interface 38 also enablesthe radiologist or other user to operate a camera controller 40 toconfigure the nuclear camera 10, initiate and control data acquisitionusing the camera 10, and the like.

For exemplary medical imaging by single photon emission computedtomography (SPECT), a human subject is administered a suitableradiopharmaceutical or radioisotope such as ^(99m)Tc or ²⁰¹T1 prior toimaging. The radiopharmaceutical is tailored to concentrate in an organof interest, or in the blood stream, or in another region of clinicalinterest. The radiopharmaceutical emits a low level of radiation, whichthe gamma detector or detectors 20 receive when the patient is insertedinto the bore 16. The gamma camera 10 acquires projection views over180°, 360+, or another selected angular range of viewing angles as therotating gantry 12 moves the gamma detector- or detectors 20 around theimaging region.

Optionally, the radiological imaging apparatus 8 includes a secondimaging modality apparatus 50, such as a positron emission tomography(PET) scanner, a computed tomography (CT) scanner, or a second nuclearcamera A second generally circular rotatable gantry 52 is disposed in asecond generally toroidal stationary housing 54. The stationary housing54 defines a second generally cylindrical bore 56. For imaging using thesecond imaging modality apparatus 50, the subject support couch 18extends to insert the subject into the second bore 56. At least onesuitable radiation detector 60 (shown by partial cutaway of theenclosing housing 54) is mounted on the second rotatable gantry 52 androtates therewith at a fixed viewing radius RI relative to an isocenter62 of a second imaging region defined by the second bore 56. The fixedviewing radius R′ may be the same or different from the fixed viewingradius R of the gamma detector or detectors 20.

For PET imaging, at least two radiation detectors are mounted andconfigured to perform coincidence gamma ray detection. For CT imaging,an x-ray source generates an x-ray beam that passes through theisocenter 62 and is detected by an x-ray detector array. The secondimaging modality apparatus 50 also includes a data memory 130, imagereconstruction processing components 132, and an image memory 134 whichcorrespond to the components 30, 32, 34. The video processor 36 adds aspatial offset corresponding to the distance between the gantries andcombines the reconstructed images for display. Optionally, data from thetwo imaging modalities can be combined prior to reconstruction.Preferably, the user interface 38 communicates with a controller 140 forthe second gantry 50. Optionally, the memory components 30, 34 can bepartitioned or otherwise configured to store data produced by eachapparatus 10, 50, and a single reconstruction processor can reconstructboth data of both imaging modalities.

To mechanically integrate the imaging apparatuses 10, 50, the isocenters22, 62 are preferably aligned on a common gantry axis 66. A prone humansubject lying on the subject support couch 18 can be moved parallel tothe common gantry axis 66 into one or the other of the bores 16, 56 forimaging using a selected one or both of the imaging apparatuses 10, 50.The rotating gantries 12, 52 rotate about the common gantry axis 66.Preferably, an axial separation f the isocenters 22, 62 along the commongantry axis 66 is calibrated such that after imaging using oneapparatus, the subject can be transferred over to the other apparatusand imaged at the same axial position.

Moreover, it will be appreciated that a third, fourth, or more imagingmodalities can be similarly integrated in the multiple imaging modalityradiological imaging apparatus 8. Each imaging modality includesradiation detectors and radiation sources appropriate to that imagingmodality arranged on a rotating gantry inside a toroidal housing thathas a cylindrical bore large enough to admit imaging subjects over arange of sizes. It will also be appreciated that, although separatetoroidal housings 14, 54 are shown in FIG. 1, a single axially extendedtoroidal housing could be used which encompasses both imagingapparatuses 10, 50.

With continuing reference to FIG. 1 and with further reference to FIG.2, imaging is performed using the gamma camera 10 with the gammadetector or detectors 20 at the fixed viewing radius R. To obtain aselected resolution, imaging time, and detection sensitivity at thefixed viewing radius R, a slat-collimated gamma detector 20 is employed,in which a slat collimator 70 and radiation detector 72 are designed toprovide the selected resolution, imaging time, and detection sensitivitycharacteristics. The slat collimator 70 includes a plurality ofgenerally parallel slats 74 of thickness W_(x) and width W_(y) separatedby gaps G. Each slat has a slat height W_(z) extending away from theradiation detector 72 toward an imaging region 76. Optionally, the slatstilt uniformly by a few degrees in the same direction.

The radiation detector 72 has dimensions of width Cy parallel to theslats 74, and length L perpendicular to the slats 74. Each adjacent slatpair defines a viewing plane that is generally transverse to theradiation detector 72 and is viewed by a generally linear element arrayof the radiation detector 72. For example, slats 74 ₁, 74 ₂ collimate aviewing plane 80 of the imaging region 76. A generally linear radiationdetector region 82 of the radiation detector 72 views the plane 80through the adjacent slats pair 74 ₁, 74 ₂.

In a preferred embodiment, the radiation detector 72 includes arectangular array of about 3,000 cadmium zinc telluride (CZT) detectorelements each sized at about 3.2 mm×1.8 mm. Each CZT detector elementincludes an electrically biased photodetector that acquires electricalcharge and produces current pulses responsive to incident gamma rays. Toprovide separable three-dimensional voxel sampling for imagereconstruction, the slat-collimated gamma detector 20 is rotated or spunby a rotary motor 86 about a slats rotation axis 88 that isperpendicular to the common gantry axis 66. Typically, for each gantryangular view, plane integral projections are acquired for a 180° or 360°span of slats spin about the slats rotation axis 88.

The fixed viewing radius R is generally substantially larger than anaverage viewing radius of a conformal gamma detector orbit. As is knownin the art, as the viewing distance between the gamma detector and theimaging region increases, imaging resolution degrades. In a conventionalgamma detector that employs a bore hole collimator, imaging resolutiondegradation can be countered by increasing collimation (e.g., byextending the collimator height toward the imaging region or by usingsmaller collimation openings). However, the increased collimationreduces detector sensitivity by reducing radiation collection efficiency(a higher percentage of radiation is absorbed by the collimator and doesnot reach the detector). Nuclear cameras heretofore have employedconformal non-circular gamma detector orbits that closely followexternal contours of the imaging subject to minimize detector viewingdistances and collimation.

The slat-collimated gamma detector 20 is preferably configured for aselected resolution and detector sensitivity over a selected imagingtime by independently tailoring resolution via the collimation (e.g.,the slat height W_(z) or the slat separation G) and detector sensitivityvia the width C_(y) of the radiation detector 72. In general, as thegamma detector 20 is moved away from the imaging region 76, theresultant degradation of the imaging resolution is countered byincreasing the collimation (e.g., increasing the slat height W_(z)). Thedetector sensitivity is maintained by increasing the detector widthC_(y) to compensate for the increased viewing distance and collimation.For a selected viewing radius R, imaging resolution, detectorsensitivity, and imaging time, optimized values of the collimation anddetector width C_(y) are determined.

More specifically, the imaging resolution generally scales linearly withviewing radius for a given collimation. That is: $\begin{matrix}{{{Imaging}\quad{resolution}} \propto \frac{R}{W_{z}}} & (1)\end{matrix}$

where R is the viewing radius R shown in FIG. 1, W_(z) is the detectorwidth W_(z) shown in FIG. 2, and a smaller value for the ratio R/W_(z)corresponds to increased or better imaging resolution. If, for example,a conformal non-circular detector orbit provides a certain imagingresolution at an average viewing radius of 20 cm, then to move to aconstant circular detector orbit with a viewing radius of 30 cm (whichis sufficient to admit most human subjects in a prone position) withoutdegrading resolution, the height W_(z) of the collimator slats 74 shouldbe increased by a factor of (30 cm÷20 cm) or 1.5 to provide the sameresolution at a 30 cm fixed-radius orbit as is obtained using aconformal non-circular orbit with an average radius of about 20 cm.Rather than increasing the slat height W_(z), the slat separation G caninstead be decreased to provide the increased collimation at constantradius of 30 cm.

Increasing the viewing radius R reduces detector sensitivity.Furthermore, increasing the collimation also reduces detectorsensitivity. For the slat-collimated gamma detector geometry, thedetector sensitivity is approximately related to slat height W_(z) andviewing radius R according to: $\begin{matrix}{{{Detector}\quad{sensitivity}} \propto \frac{1}{W_{z}^{2} + \left( {W_{z} \cdot R} \right)}} & (2)\end{matrix}$where a larger value for Equation (2) corresponds to better detectorsensitivity. Hence, for the exemplary increase of the viewing radiusfrom 20 cm to 30 cm and a corresponding proportional increase in slatheight W_(z) of 1.5, the detector sensitivity is proportionately reducedby a factor of 2.25. To compensate for this sensitivity loss, theradiation detector width C_(y) is suitably proportionally increased by afactor of 2.25.

In summary, the gamma camera 10 of FIG. 1 using the slat-collimatedgamma detector 20 illustrated in FIG. 2 provides substantially similarresolution and detector sensitivity at a constant viewing radius R of 30cm as compared with a conformal gamma camera orbit in which the detectororbits conformally at an average radius of 20 cm. The increased distancefrom 20 cm to 30 cm is compensated by scaling up the slat height W_(z)by a factor of 1.5, and by scaling up the detector width C_(y) by afactor of 2.25. By making these adjustments, imaging at 30 cm fixedradius for a reasonable imaging time, such as about 20 minutes, providessubstantially equivalent resolution and detector sensitivity as a 20minute conformal imaging session at an average viewing radius of about20 cm. With the conformal orbiting of the gamma detectors eliminated,the enclosing housing 14 is preferably included to improve aestheticappearance of the gamma camera 10, to be comparable in aspect, shape,and size with other imaging modalities (CT, PET and MNW, to shield themoving gamma detector or detectors 20 and rotating gantry 12 from view,and to prevent contact with moving gamma camera components.

With reference to FIG. 3, another advantage of the constant radius R isthat more than three gamma detectors can be simultaneously used foracquiring imaging data. For example, as shown in FIG. 3, four gammadetectors 20 can be mounted on the rotating gantry 12 and simultaneouslyused for imaging data acquisition. Each of the four detectors 20 ispositioned at the viewing distance R from the isocenter 22 of therotating gantry 12, and so do not interfere with one another. More thanfour detectors can similarly be employed. In contrast, when a conformalgamma detector orbit such as has been practiced heretofore is used, onlythree or fewer simultaneously operating gamma detectors is practicable.This is because geometrical constraints substantially hinder conformalnon-circular orbiting about an imaging subject by four or moredetectors. With four or more conformally non-circularly orbitingdetectors, the detectors will generally impinge upon one another atvarious positions within the orbit. The additional gamma detectors canbe used to collect redundant imaging data, or to provide 360° of gantryangular imaging views with a gantry rotation of less than 360°. For theexemplary four detectors 20 shown in FIG. 3, a 90° gantry rotationprovides 360° of angular coverage.

With continuing reference to FIG. 3, yet another advantage of theconstant radius gamma camera 10 is improved symmetry of the imaging. Forexample, the four gamma detector arrangement of FIG. 3 has at least afour-fold rotational symmetry and four reflection symmetry planes. Thishigh degree of symmetry can be used to improve radiation detectionefficiency, simplify image reconstruction complexity, and reduce imagereconstruction time. The inverse distance dependence of slat-collimatedplane integral projection views is simplified by the circular orbitsince the detector viewing radius R is a constant throughout thedetector orbit. As yet another option, additional heads (shown inphantom) can be added to encircle the subject more completely.Increasing the number of detector heads increases counts which improvesimage quality or reduces data collection time.

With reference to FIG. 4, still yet another advantage slat-collimatedgamma detectors orbiting at a constant radius R₂ is that the spinning orrotation of the slats 70 about the slats rotation axis 88 can besubstantially angularly limited. FIG. 4 shows six gamma detectors 20 ₁,20 ₂, 20 ₃, 20 ₄, 20 ₅, 20 ₆ spaced at 60° intervals around a rotatinggantry 12′. For a 360° rotation of the gantry 12′ about the commongantry axis 66, each of the six gamma detectors 20 ₁, 20 ₂, 20 ₃, 20 ₄,20 ₅, 20 ₆ will traverse every gantry angular view. In other words, foreach angular position around the gantry, each of the six gamma detectors20 ₁, 20 ₂, 20 ₃, 20 ₄, 20 ₅, 20 ₆ views from that angular position atsome interval of the 360° gantry rotation. Hence, the 360° spin of theslats about the slats rotation axis 88 is optionally divided among thesix gamma detectors 20 ₁, 20 ₂, 20 ₃, 20 ₄, 20 ₅, 20 ₆.

In one suitable arrangement: slats of gamma detector 20 ₁ spin between0° and 60°; slats of gamma detector 202 spin between 60° and 120°; slatsof gamma detector 20 ₃ spin between 120° and 180°; slats of gammadetector 204 spin, between 180° and 240°; slats of gamma detector 205spin between 240° and 300°; and slats of gamma detector 206 spin between300° and 360°, all around the slats rotation axis 88. Because thespinning of the slats about the axis 88 for each gamma detector spansonly 60°, the rotary motor 86 shown in FIG. 2 can be replaced by alinear arm actuator, which simplifies mechanical construction of theslat-collimated gamma detectors.

With returning reference to FIG. 1, the multiple imaging modalityradiological imaging system 8 provides SPECT imaging through the gammacamera 10 and another imaging modality such as PET or CT through thesecond imaging modality apparatus 50. For a calibrated separation of theisocenters 22, 62 of the two rotating gantries 12, 52, switching betweenthe two imaging modalities can be rapidly and conveniently performed bycalibrated axial movement of the patent support 18. However, it Dialseparation of the gantries 12, 52 precludes simultaneous imaging at thesame axial position using the two imaging modalities.

With reference to FIG. 5, a gantry 12″ provides simultaneous SPECT andsecond-modality imaging at the same axial position. Four SPECT gammadetectors 20′ are arranged on a circular rotating gantry 12″ at aviewing distance R₃ from a gantry isocenter 22″. This arrangement issubstantially similar to the arrangement of gamma detectors 20 on therotating gantry 12 shown in FIG. 3. The fixed-radius circular orbitingof the SPECT gamma detectors 20′ enables interleaving of additionalradiation detectors 94 between the SPECT gamma detectors 20′ on therotating gantry 12″. In FIG. 5, four PET detectors 94 are arranged onthe gantry 12″, viewing the isocenter 22″ at a distance R₄ which may bethe same as or different from the viewing distance R₃ of the SPECT gammadetectors 20′. The uncollimated PET detectors 94 suitably acquirecoincidence PET data simultaneously with acquisition of SPECT data bythe gamma detectors 20′.

With reference to FIG. 6, in a similar fashion, a computed tomographyscanner is integrated onto a fixed-radius gamma camera employingslat-collimated detectors 20′ arranged on a gantry 12′″ about an imagingisocenter 22′″ at a viewing radius R₅. The computed tomography scannerincludes an x-ray source 96 and an oppositely disposed x-ray detectorarray 98. In the single-gantry SPECT/CT system, simultaneous acquisitionof SPECT data and CT data is complicated by a large difference inoptimal rotation rates for the CT and SPECT imaging modalities,different radiation intensities, scattered radiation, and the like.However, the preferred CZT detectors 72 of the slat-collimated SPECTgamma detectors 20″ are advantageously resistant to damage by scatteredhigh-intensity x-rays when they are shut off, and so SPECT and CT can beacquired sequentially without moving the subject support 18 and withoutshuttering the SPECT gamma detectors 20″ during operation of the x-raytube 96. Alternatively, the source 96 can be an isotope source.

Other imaging modalities can be similarly integrated onto a singleconstant-radius SPECT gantry. For example, dissimilar gamma detectors ordifferently collimated gamma detectors can be interleaved on the gantryto provide different imaging resolutions, differently optimized spectralcharacteristics, or the like. Similarly, a transmission-mode SPECTsystem including a suitable gamma radiation source and dedicatedreceiving gamma detector can be integrated onto the gantry.

The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations insofar as they come within thescope of the appended claims or the equivalents thereof.

1. A nuclear camera including: a rotatable gantry defining a gantry rotation axis Band an imaging isocenter; and a gamma detector arranged on the rotating gantry at a fixed radial distance from the imaging isocenter, the gamma detector including a radiation-sensitive surface and a collimator that collimates incoming radiation.
 2. The nuclear camera as set forth in claim 1, wherein the collimator includes: a plurality of spaced-apart slats arranged transverse to the radiation-sensitive surfaces, each adjacent slat pair defining a viewing plane.
 3. The nuclear camera as set forth in claim 2, wherein the gamma detector further includes: a means for spinning the collimator slats and the radiation sensitive surface about a slat rotation axis that is generally orthogonal to the gantry rotation axis.
 4. The nuclear camera as set forth in claim 3, wherein: the slats have a spacing and height selected based on a selected spatial imaging resolution, a predetermined imaging time, and the fixed radial distance; and a width of each generally linear detector is selected based on a selected detector sensitivity, the predetermined imaging time, the fixed radial distance, and the slat pair.
 5. The nuclear camera as set forth in claim 4, wherein the slat height in a direction transverse to the radiation-sensitive surface corresponds to a ratio of the fixed radial distance and the selected spatial imaging resolution.
 6. The nuclear camera as set forth in claim 3, wherein the radiation-sensitive surface includes an array of solid state detector elements.
 7. The nuclear camera was set forth in claim 6, further including: a radiation source disposed on the rotatable gantry and producing transmission radiation; and an transmission radiation detector mounted opposite the radiation source that detects the transmission radiation.
 8. The nuclear camera was set forth in claim 1, further including at least four gamma detectors mounted at the fixed radial distance from the imaging isocenter.
 9. The nuclear camera as set forth in claim 8, further including: at least a pair of radiation detectors oppositely mounted on the rotatable gantry that are configured to perform coincidence detection of radiation emitted during positron-electron annihilation.
 10. The nuclear camera as set forth in claim 8, wherein the: the gamma detectors are collimated for at least two different imaging resolutions.
 11. The nuclear camera as set forth in claim 1, further including: a generally toroidal housing substantially enclosing the rotatable gantry and the gamma detector.
 12. The nuclear camera as set forth in claim 11, further including: a second generally toroidal housing holding a second imaging modality, the second generally toroidal housing being mounted a fixed distance from the first generally toroidal housing.
 13. A nuclear camera including: at least four SPECT radiation detectors rotatably arranged around an imaging region to receive emission radiation, the radiation detectors each disposed an equal distance from an imaging isocenter, the radiation detectors each including a radiation-sensitive surface that responds to the first emission radiation; a slat collimator disposed on each radiation detector between the radiation detector and the imaging region to provide planar collimation of incoming first emission radiation; and a means for spinning the collimator and radiation-sensitive surface of each SPECT radiation detector about a detector axis.
 14. The nuclear camera as set forth in claim 13, further including: a generally circular rotatable gantry on which the radiation detectors are disposed; and an optically opaque housing that is substantially transmissive for the first emission radiation.
 15. The nuclear camera as set forth in claim 13, further including radiation detectors configured for at least one of a different SPECT resolution and a different imaging modality.
 16. The nuclear camera as set forth in claim 13, further including: a computed tomography scanner including a transmission radiation source and a transmission radiation detector disposed opposite the transmission radiation source on the rotatable gantry.
 17. A radiological imaging method including: circularly orbiting at least one radiation detector about an imaging volume at a fixed radial distance from a first axis of rotation through the imaging volume; and detecting radiation from the imaging volume at a generally planar radiation-sensitive region of the radiation detector, the radiation-sensitive region facing the imaging volume during the fixed radius circular orbiting.
 18. The radiological imaging method as set forth in claim 17, further including: during the circular orbiting, spinning a slat collimator and a radiation-sensitive array about an axis perpendicular to the first axis of rotation; integrating radiation detected over generally planar regions defined by the slat collimator to generate plane integral projection views; and reconstructing an image representation of the imaging volume from the plane integral projection views.
 19. The radiological imaging method as set forth in claim 18, wherein the orbiting rotates each of a plurality of detectors to common locations M times, where M is an integer, and the collimator and radiation-sensitive array are spun one of 180°/M and 360°/M at each location.
 20. The radiological imaging method as set forth in claim 18, further including: selecting a minimum width of the generally planar radiation-sensitive array in a direction parallel to the generally planar regions to provide a selected radiation detection sensitivity.
 21. The radiological imaging method as set forth in claim 17, wherein the orbiting includes: orbiting a plurality of radiation detectors an angle of 180° divided by the number of radiation detectors.
 22. The radiological imaging method as set forth in claim 21, further including: selecting at least one of collimator slat spacing and collimator height in accordance with a selected resolution and the fixed radial distance.
 23. The radiological imaging method as set forth in claim 17, further including: disposing a radiation-transmissive, optically opaque shield between the at least one radiation detector the imaging volume, the shield remaining stationary during the circular orbiting and blocking optical communication between the imaging volume and the radiation detector during the circular orbiting.
 24. The radiological imaging method as set forth in claim 17, further including: orbiting at least four radiation detectors at the fixed radial distance.
 25. The radiological imaging method as set forth in claim 24, wherein the detectors include SPECT detectors collimated for a first resolution and at least one of: a SPECT detector collimated for a second resolution, a pair of PET detectors, and a transmission radiation detector.
 26. An imaging apparatus comprising: a rotatable gantry defining a gantry rotation axis and an imaging isocenter; three or more gamma detectors arranged on the rotatable gantry at a fixed radial distance from the imaging isocenter; a collimator located on each of said three or more gamma detectors: and a means for processing data detected by said three or more gamma detectors to produce an image.
 27. The imaging apparatus of claim 26 wherein each of the collimators includes a plurality of spaced-apart slats and a means for spinning the collimator slats about a slat rotation axis.
 28. An imaging apparatus comprising: at least four SPECT radiation detectors rotatably arranged around an imaging region, each detector disposed an equal distance from an imaging isocenter, wherein each detector includes: a slat collimator, wherein at least one of collimator slat spacing and collimator height are selected to provide a predetermined resolution at said fixed distance; and a detector width selected to provide a predetermined radiation detection sensitivity at said fixed distance.
 29. The imaging apparatus of claim 28 wherein said predetermined resolution and said predetermined radiation detection sensitivity are approximately equal to or greater than the resolution and detection sensitivity of a conformal, non-circular SPECT detector.
 30. The imaging apparatus of claim 28 wherein each slat collimator includes a plurality of spaced-apart slats and a means for spinning the collimator slats about a slat rotation axis. 